Make rubocop happy

- Use instance variables
- Remove redundant one-character regex classes

lib/gitlab/usage/metric_definition.rb

@@ -42,7 +42,7 @@ module Gitlab
         end
 
         def definitions(skip_validation: false)
-          @@skip_validation = skip_validation
+          @skip_validation = skip_validation
           @definitions ||= load_all!
         end
 
@@ -88,7 +88,7 @@ module Gitlab
       end
 
       def skip_validation?
-        !!attributes[:skip_validation] || @@skip_validation
+        !!attributes[:skip_validation] || @skip_validation
       end
     end
   end

spec/lib/generators/gitlab/usage_metric_definition/redis_hll_generator_spec.rb

@@ -13,14 +13,14 @@ RSpec.describe Gitlab::UsageMetricDefinition::RedisHllGenerator do
   before do
     stub_const("#{Gitlab::UsageMetricDefinitionGenerator}::TOP_LEVEL_DIR", temp_dir)
     # Stub Prometheus requests from Gitlab::Utils::UsageData
-    stub_request(:get, %r{^http[s]?://::1:9090/-/ready})
+    stub_request(:get, %r{^https?://::1:9090/-/ready})
       .to_return(
         status: 200,
         body: [{}].to_json,
         headers: { 'Content-Type' => 'application/json' }
       )
 
-    stub_request(:get, %r{^http[s]?://::1:9090/api/v1/query\?query=.*})
+    stub_request(:get, %r{^https?://::1:9090/api/v1/query\?query=.*})
       .to_return(
         status: 200,
         body: [{}].to_json,